Attention, millionaires, the watchful eye of the Internal Revenue Service is trained on you. During last year's tax season, 30% of multimillionaires were audited, the agency said. Overall, just 1.1% of individual income tax returns were checked.

Taxpayers making an adjusted gross annual income of $10 million or more are increasingly on the IRS' radar -- in 2010, just 18% of them faced audits, according to a report from the agency. Nearly 21% of Americans making between $5 and $10 million had their returns inspected, the IRS said; 12% of millionaires making less underwent the same process.

From Oct. 1, 2010, through Sept. 30, 2011, the agency said it collected $2.4 trillion in taxes from 234 million processed returns, up from the $2.3 trillion collected the year before. It was the first year of increased revenue since 2008.

The IRS said more than 133 million tax returns -- including more than three-quarters of all individual returns -- were filed online. More than eight in 10 individual returns resulted in refunds -- a total payout of $338 billion (among all tax returns, nearly $415.9 billion was refunded).

Nearly 4,700 criminal investigations were completed last year, the agency said, with 1,802 resulting in incarcerations.

Nearly 28 million returns, or $281.2 billion in gross collections, came from California -- the most of any state. Nearly 13.9 million refunds, or $47 billion, went to taxpayers.

For the record, 4 p.m., March 23: A previous version of this post said $281.2 million in gross collections came from California. The number is $281.2 billion. And $47 billion, not $47 million, was paid out in refunds to California taxpayers.